1. Field of the Invention
The present invention relates to flame retardant polyvinyl chloride ("PVC") resin compositions and more particularly to PVC resin compositions incorporating polybrominated higher alkylbenzenes.
2. Description of the Prior Art
Traditionally, most flame retardants, although efficient in their function of retarding the rate of combustion in a resin system, have a tendency to affect adversely one or more key properties of the resin. For example, many flame retardant additives tend to reduce impact strength of the resin; to migrate from the resin composition, resulting in a phenomenon known as "spew"; to volatilize from the resin composition; to plasticize the resin composition adversely, thus lowering the heat deflection temperature, etc.
It is therefore essential that a flame retardant agent be specifically tailored to the resin system so that, in addition to its role as a flame retardant, the agent will additionally enhance the desirable characteristics of the resin composition. Those skilled in the art well know that the selection of such an application-specific flame retardant is unpredictable at best. Thus, even though a given agent may exhibit utility in a particular resin system, that is no guarantee that this agent will have any use at all With other resins.
Among the PVC markets requiring flame retardance are wall coverings, mine belting, film and sheeting, cellular insulation, wire and cable insulation and coated fabrics. Although PVC is naturally flame retardant due to its chlorine content, these applications require plasticization of the resin in order to achieve the desired properties. The most common plasticizers used in PVC are classified as phthalates, aliphatic diesters, phosphates, and trimellitates. Unfortunately all of these plasticizers are either volatile, non-flame resistant, thermally unstable or have a tendancy to migrate.
A family of thermally stable halogenated phthalate PVC plasticizers is disclosed in U.S. Pat. Nos. 4,298,517, 4,397,977 and 4,098,704. However, these materials are not entirely satisfactory because, in addition to being only average plasticizers, they suffer from excessive spew and are quite thermally unstable.
Underwood, et al. U.S. Pat. No. 3,850,882 discloses a three component flame retardant additive system for polyolefins, especially polypropylene, consisting of
(a) among other halogenated materials, a halogenated alkyl benzene of the formula ##STR1## where X may be Cl or Br; and Y is a hydrocarbon of 1-20 carbon atoms; a is an integer from 0 to 3; and n is an integer from 3 to 6;
(b) stannic oxide; and
(c) a bis-phenylalkylene hydrocarbon.
The patent does not suggest that such a flame retardant mixture has any utility in PVC resins, let alone that the halogenated alkylbenzene would have any such use.
Rueter, et al. U.S. Pat. No. 4,129,551 discloses nonflammable polyester compositions incorporating a phosphorus-containing, multiple component flame retardant additive consisting of:
(a) a triarylphosphine oxide or an aryl or alkyl ester of an arylphosphinic acid;
(b) a nuclear brominated alkylbenzene; and
(c) customary auxiliary agents and additives.
Polyester compositions based on such agents contain 0.5-10% by weight of bromine and 0.1-2% by weight of phosphorus. Among the nuclear brominated alkylbenzenes described were compounds of the following formula: ##STR2## where x=2 to 5, y and z each are zero or an integer from 1 to 17 and sum of y+z is an integer between 7 and 17 or a mixture thereof.
Mixtures of such agents are also suggested. There is no disclosure that the additive mixture has any utility in PVC resins or that the nuclear brominated alkylbenzene may be so-used alone for that or any other purpose.
Thus, a primary objective of this invention is to provide halogenated resin compositions incorporating superior flame retardant plasticizing agents.
A further object is to provide flame retardant plasticizers for PVC resin compositions that are flame resistant, non-volatile, thermally stable and which do not migrate.
Yet a further object is to utilize polybrominated higher alkylbenzenes as flame retardant plasticizers for PVC resin compositions.